CG Simulation of Dislocations


Research Areas:

Link Atomistic to Continuum 
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CG Simulation of Dislocations 

Multiscale Thermal Transport
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Dislocation-Interface Interactions
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Bio-inspired Composites
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Materials under Irradiations
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Brittle-to-Ductile Fracture
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High-pressure Phase Transitions
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Nanostructured Ceramics 
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Most of the existing coarse-grained (CG) atomistic methods begin with the construction of an effective Hamiltonian or potential energy as a function of the degrees-of-freedom of representative atoms. Then the energy is minimized to find the equilibrium state. Distinct from the existing CG methods, a novel coarse-grained atomistic approach was developed by Dr. Xiong and his coworkers. The fundamental difference between this new approach and existing CG methods is that we start with a full set of field representation of balance equations in terms of  atomic variables, and then solve the balance equations using an finite element (FE) method. To model dislocations in fcc- or diamond-crystal, a rhombohedral-shaped FE was adopted to mimic the shape of the primitive unit cell of those crystals. Such an element (figures shown above) ensures that, following nucleation, dislocations can glide between elements on either of two slip systems along element boundaries, inspite of the approximation that the displacement field within each FE is interpolated from nodal displacement using a shape function. Our CG models were demonstrated to be capable to simulate the formation of dislocation networks, nucleation and growth of dislocation loops from nanometers to sub-microns (figures shown below).


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Recently, in our group, the CG models were applied to characterize the complex dislocation elastodynamics, including the energy intensity and the wavelength of phonon waves emitted from fast moving dislocations, and the velocity-dependent core stress field, in anisotropic crystalline materials subjected to an intermediate and high strain rate loading. Mach cones in a V-shaped pattern of the phonon wave-fronts are observed in the wake of the supersonic dislocations (figures and movies as shown below). Our CG approach was demonstrated to be a predictive multiscale method that explicitly treats the strong coupling between the long-range elastic field away from the dislocation core, the highly nonlinear time-dependent stress field within the core, and the reconfiguration of the dislocation core structure.


References:

  • Xiong, L., Tucker, G., McDowell, D.L., and Chen, Y., 2011. Coarse-grained atomistic simulation of dislocations, Journal of Mechanics and Physics of Solids, 59, 2, 160-177. doi:10.1016/j.jmps.2010.11.005
  • Xiong, L., McDowell, D.L., and Chen, Y., 2012. Nucleation and growth of dislocation loops in Cu, Al, and Si by a concurrent atomistic-continuum method, Scripta Materialia, 67, 633-636.  doi:10.1016/j.scriptamat.2012.07.026
  • Xiong, L., Rigelesaiyin, J., Chen, X., Xu, S., McDowell, D.L., and Chen, Y., 2016. Coarse-grained elastodynamics of fast moving dislocations, Acta Materialia, 104, 143-155. doi:10.1016/j.actamat.2015.11.037

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